Increasing world populations and dwindling productive farm land place increasing demands on agricultural efficiency. The sustainability of agriculture demands that production per unit area of land be increased in a cost-effective manner. It has long been the goal of growers to be able to manipulate the vegetative and reproductive growth of plants to increase the quantity and quality of crops. Cultivars of vegetable, fruit, nut, grain, forage and ornamental crops are no exception. Total yield is expressed as a function of quantity and mass as the product of organ (e.g., root, stem, leaf, flower, seed and fruit) or plant number multiplied by organ or plant weight. Thus, an increase in total crop yield may result from an increase in quantity, an increase in mass, or a combination of the two. As growers strive to increase profitability of their farm lands, quantity and size has become increasingly important. This is increasingly important in the production of fruit and nut crops. Accordingly, since consumers tend to prefer large size fruit and nuts, they are commercially more valuable than small size fruit and nuts.
Total yield of vegetable, fruit, nut, grain, forage and ornamental crops is affected by many factors. For instance, fruit quantity is dependent on flower number and the number of branches capable of bearing flowers, while fruit size is dependent on the number of fruit set. Seed production influences both the number of fruit set and fruit size. Fruit size is also influenced by the number of leaves exporting the products of photosynthesis to the fruit. Root, tuber and bulb crops are similarly affected by the number of leaves exporting photosynthate to the below ground portions of the plant. Above and below ground parts of the plant produce hormones that further affect plant growth and crop yield. Root development, nutrient uptake, water availability, climate and stress (abiotic and biotic) all affect photosynthesis and plant metabolism and hence fruit size. Additionally, all aspects of production are affected by agricultural practices such as pruning, fertilization, irrigation and use of nutritional supplements and plant growth regulators.
At the present time, plant growth regulators (PGRs) are one of the most powerful tools available for manipulating the vegetative and reproductive growth of crop plants. For a wide variety of annual, biennial and perennial crops, PGRs have been used to solve production problems. For example, PGRs have been used successfully as foliar sprays to increase flowering, synchronize bloom, or change the time of flowering to avoid adverse climatic conditions or to shift harvest to a time when the market is more economically favorable. Foliar-applied PGRs are routinely used to improve fruit set, reduce June drop or to prevent pre-harvest drop to increase yield. PGR sprays are applied to increase fruit size directly by stimulating cell division. Application of a PGR that reduces the number of flowers formed or promotes flower or fruit abscission increases fruit size indirectly by decreasing fruit number. PGRs have been used as both pre- and post-harvest treatments to hasten or slow the ripening process, color development, and maturation of specific tissues to improve the quality of the product sold in the market. An emerging use of PGRs is for overcoming the adverse effects of abiotic stresses. Surprisingly, these successes have been achieved with a modest number of commercial PGRs that are members of or impact the synthesis of one of five classic groups: auxins, cytokinins, gibberellins, abscisic acid and ethylene.
However, as many PGRs are synthetic chemical compounds that mimic the effects of natural plant hormones, they are subject to regulation under the Federal Insecticide, Fungicide, and Rodenticide Act, administered by the United States Environmental Protection Agency. In addition to the regulatory hurdles faced by PGRs, their use is not favorably received by a growing segment of consumers who prefer organic produce. As such, what the art needs are compositions and methods that employ natural compounds to increase crop production.